l&t fast bus transfer system

Fast Bus Transfer Fast Bus Transfer SystemSystem

P K SharmaP K Sharma

FBT- Normal System ConfigurationsFBT- Normal System Configurations

Methods of supply transferMethods of supply transfer

► Parallel TransferParallel Transfer► Fast TransferFast Transfer►Delayed TransferDelayed Transfer

Parallel TransferParallel Transfer- - Widely used method for unit Widely used method for unit

start up and planned shut-start up and planned shut-down using a synchro-check down using a synchro-check relay.relay.

Advantages:Advantages: Transients on motors are Transients on motors are

avoided.avoided.

Disadvantages:Disadvantages:

If a bus fault occurs during If a bus fault occurs during transfer, though the transfer, though the probability is low, then swgr probability is low, then swgr fault with-stand capacity may fault with-stand capacity may be violated causing damage be violated causing damage to generator, motors and to generator, motors and transformer.transformer.

Equipment Required: A synchronizing relay .

Fast TransferFast Transfer

- Open UAT CB before closing SST CB or issue trip and - Open UAT CB before closing SST CB or issue trip and close commands simultaneously and use fast 52b close commands simultaneously and use fast 52b contact of UAT to SST breaker closing circuit.contact of UAT to SST breaker closing circuit.

Advantages:Advantages:

Problems of parallel operation is avoided.Problems of parallel operation is avoided.

Disadvantages:Disadvantages:

If UAT CB is slow in opening then the problems of If UAT CB is slow in opening then the problems of parallel transfer may occur.parallel transfer may occur.

Equipment Required: A fast acting synchronizing relay, fast enough to check that the phase angle between 2 voltages is within acceptable limit.

Delayed TransferDelayed Transfer► In-Phase TransferIn-Phase Transfer

This is a high speed This is a high speed synchronization between synchronization between motor bus and SST such motor bus and SST such that the up coming that the up coming breakers’ contacts close breakers’ contacts close at the time of zero at the time of zero incidence.incidence.

► Residual Voltage TransferResidual Voltage Transfer

Slowest transfer.Slowest transfer.

Wait until motor bus falls to a Wait until motor bus falls to a Low level say 25%.Low level say 25%.

But, all motors will drop out But, all motors will drop out byby

this time and all motors can this time and all motors can not be restarted together so not be restarted together so shedding some motor load shedding some motor load

and and re-starting these makes itre-starting these makes it complicated.complicated.

L&T Fast Bus Transfer SystemsL&T Fast Bus Transfer SystemsSCX SCX system is designed to allow fast auto or manual system is designed to allow fast auto or manual transfer of supply systems by comparing input transfer of supply systems by comparing input parameters and compare them with set values and parameters and compare them with set values and execute transfer as quickly as possible (of the order execute transfer as quickly as possible (of the order of 30 ms). This helps in reducing stress on Induction of 30 ms). This helps in reducing stress on Induction motors.motors.

► Model SCX1Model SCX1 for one synchro-check and 2 control for one synchro-check and 2 control modules. (2:I/C system), modules. (2:I/C system), most-widely used.most-widely used.

► Model SCX2Model SCX2 with two synchro-check and 3 control with two synchro-check and 3 control modules. (2:I/C +1:B/C systems)modules. (2:I/C +1:B/C systems)

► Model SCX3Model SCX3 with three synchro-check and 4 control with three synchro-check and 4 control modules. (3:I/C +2:B/C systems). modules. (3:I/C +2:B/C systems). (A combination of SCX1 + (A combination of SCX1 + SCX2)SCX2)

SCX system featuresSCX system features

► Transfer Permissive ConditionsTransfer Permissive Conditions

-- Availability of circuit breakers.-- Availability of circuit breakers.

-- Busbar voltage and frequency.-- Busbar voltage and frequency.

-- Incomer voltage and frequency-- Incomer voltage and frequency

-- Busbar and source V & f mismatch and phase -- Busbar and source V & f mismatch and phase displacement.displacement.

-- Frequency rate of decay.-- Frequency rate of decay.

SCX1 systemSCX1 systemThe system contains a fast transfer module and for each CB, it contains:

-- CB control module to detect CB Status, trip, logic interlock, operation lock out etc.

-- Local control of CB from front fascia of the system.

-- Remote control of CB via serial port.

-- Monitoring of each input and output locally as well as via serial at remote

SCX system featuresSCX system features► Manual Transfer ControlManual Transfer Control

This can be done locally or by initiation by digital input or This can be done locally or by initiation by digital input or via serial port.via serial port.

The transfer is initiated as soon as the first acceptable The transfer is initiated as soon as the first acceptable situation occurs.situation occurs.


► Automatic Transfer ControlAutomatic Transfer Control

The transfer is initiated on tripping of protective relays or by The transfer is initiated on tripping of protective relays or by under/over voltage elements incorporated in the system. The under/over voltage elements incorporated in the system. The system opens faulty CB and closes new CB as per following:system opens faulty CB and closes new CB as per following:

1. Instantaneous transfer

If the slip between up coming source and decaying source is small enough including the CB closing time.


► Automatic Transfer ControlAutomatic Transfer Control

The transfer is initiated on tripping of protective relays or by The transfer is initiated on tripping of protective relays or by under/over voltage elements incorporated in the system. The under/over voltage elements incorporated in the system. The system opens faulty CB and closes new CB as per following:system opens faulty CB and closes new CB as per following:

2. Transfer at first voltage match after taking care of

CB closing time.

3. If above condition also does not exist, then the transfer takes

place if residual voltage falls below set level.

4. The transfer can be programmed to take place after a pre-set time delay.


► Plausibility CheckPlausibility Check

If the open and close signals are simultaneously If the open and close signals are simultaneously present or absent for longer than a set time Tc , present or absent for longer than a set time Tc , the system produces an operation lock out and an the system produces an operation lock out and an alarm signal.alarm signal.

► Operation CheckOperation Check

If after a set time delay Tf from the emission of an If after a set time delay Tf from the emission of an open or close command, the CB does not change open or close command, the CB does not change its status, the system produces operation lockout its status, the system produces operation lockout and alarm signal.and alarm signal.

l&t fast bus transfer system

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